This invention relates generally to magnetic data storage systems, more particularly to magnetoresistive read/write heads, and most particularly to an especially compact write structure.
Magnetic disk drives are used to store and retrieve data for digital electronic apparatuses such as computers. In FIGS. 1A and 1B, a magnetic disk data storage system 10 includes a sealed enclosure 12, a disk drive motor 14, and a magnetic disk, or media, 16 supported for rotation by a drive spindle S1 of motor 14. Also included are an actuator 18 and an arm 20 attached to an actuator spindle S2 of actuator 18. A suspension 22 is coupled at one end to the arm 20, and at its other end to a read/write head or transducer 24. The transducer 24 typically includes an inductive write element with a sensor read element (both of which will be described in greater detail with reference to FIG. 2A). As the motor 14 rotates the magnetic disk 16, as indicated by the arrow R, an air bearing is formed under the transducer 24 causing it to lift slightly off of the surface of the magnetic disk 16, or, as it is sometimes termed in the art, to “fly” above the magnetic disk 16. With the arm 20 held stationary, data bits can be read along a circumferential “track” as the magnetic disk 16 rotates. Further, information from concentric tracks can be read from the magnetic disk 16 as the actuator 18 causes the transducer 24 to pivot in an arc as indicated by the arrows P. The design and manufacture of magnetic disk data storage systems is well known to those skilled in the art. 
FIG. 2A depicts a magnetic read/write head 24 including a read element 26 and a write element 28. Edges of the read element 26 and write element 28 also define an air bearing surface ABS, in a plane 29, which can be aligned to face the surface of the magnetic disk 16 (see FIGS. 1A and 1B). The read element 26 includes a first shield 30, an intermediate layer 32, which functions as a second shield, and a read sensor 34 that is located within a dielectric medium 35 between the first shield 30 and the second shield 32. The most common type of read sensor 34 used in the read/write head 24 is the magnetoresistive (AMR or GMR) sensor which is used to detect magnetic field signals from a magnetic medium through changing resistance in the read sensor.
The write element 28 is typically an inductive write element which includes the intermediate layer 32, which functions as a first pole, and a second pole 38. A first pole pedestal 42 may be connected to a first pole tip portion 43 of the first pole 32, and a second pole pedestal 44 may be connected to the second pole tip portion 45 of the second pole 38. The first pole 32 and the second pole 38 are attached to each other by a backgap 40 located distal to their respective pole tip portions, 43 and 45. The first pole 32, the second pole 38, and the backgap 40 collectively form a yoke 41 together with the first pole pedestal 42 and the second pole pedestal 44, if present. The area around the first pole tip portion 43 and the second pole tip portion 45 near the ABS is sometimes referred to as the yoke tip region 46. A write gap 36 is formed between the first pole pedestal 42 and the second pole pedestal 44 in the yoke tip region 46. The write gap 36 is formed of a non-magnetic electrically insulating material. This non-magnetic material can be either integral with (as is shown here) or separate from a first insulation layer 47 that lies between the first pole 32 and the second pole 38, and extends from the yoke tip region 46 to the backgap 40.
Also included in write element 28 is a conductive coil layer 48, formed of multiple winds 49. The conductive coil layer 48 is positioned within a coil insulation layer 50 that lies  above the first insulation layer 47. The first insulation layer 47 thereby electrically insulates the coil layer 48 from the first pole 32, while the coil insulation layer 50 electrically insulates the winds 49 from each other and from the second pole 38. In some prior art fabrication methods, the formation of the coil insulation layer includes a thermal curing of an electrically insulating material, such as photoresistive “photoresist” material.
FIG. 2B shows a plan view of the read/write head 24 taken along line 2B—2B of FIG. 2A. This view better illustrates how the coil layer 48 of write element 28 is configured as a spiral with each wind 49 passing around the backgap 40 and beneath the second pole 38 in the region between the backgap 40 and the second pole tip region 45. Because of the magnetic properties of the yoke 41, when a write current is passed through coil layer 48 a magnetic flux is induced in the first and second poles 32 and 38. The write gap 36, being non-magnetic, allows the magnetic flux to fringe out from the yoke 41, thus forming a fringing gap field. Data may be written to the magnetic disk 16 by placing the ABS of read/write head 24 proximate to the magnetic disk 16 such that the fringing gap field crosses the surface of the magnetic disk 16. Moving the surface of the magnetic disk 16 through the fringing gap field causes a reorientation of the magnetic domains on the surface of the magnetic disk 16. As the magnetic disk 16 is moved relative to the write element 28, the write current in coil layer 48 is varied to change the strength of the fringing gap field, thereby encoding data on the surface of the magnetic disk 16 with a corresponding variation of oriented magnetic domains.
Returning to FIG. 2A, a number of parameters that influence the performance of the write element 28 are also shown. The first of these parameters is the yoke length YL, sometimes defined as the distance from the backgap 40 to the first pole pedestal 42. A shorter yoke length YL favors higher data recording rates as it tends to reduce the flux rise time. The flux rise time is a measure of the time lag between the moment a current passed  through coil layer 48 reaches its maximum value and the moment the fringing flux field between the first pole 32 and the second pole 38 reaches its maximum. Ideally, the response would be instantaneous, but various factors such as the physical dimensions and the magnetic properties of the yoke 41 cause the flux rise time to increase. A shorter flux rise time is desirable both to increase the rate with which data may be written to a magnetic disk 16, and also to decrease the length of, and the spacing between, data bits on the magnetic disk 16. Shorter data bits more closely spaced together is desirable for increasing the total storage capacity of the magnetic disk 16.
Write elements according to the prior art are manufactured through common photolithography techniques well known in the art involving repeated cycles of masking with “photoresist,” depositing layers of various materials, followed by stripping away remaining photoresist. Each cycle through this process typically fabricates one element of the final structure. Consequently, tolerance for mask misalignment must be accounted for in the designs for these devices. In particular, prior art write elements leave a separation of at least 4 microns between pole pedestals 42 and 44 and the coil layer 48. A similar gap of at least 4 microns is found between the backgap 40 and the coil layer 48. These separations add extra length to the yoke length YL that increases the flux rise time and hinders write performance.
Another parameter of the write element 28 is the stack height SH, sometimes defined as the distance between the top surface of the first pole 32 and the top of the second pole 38, as shown in FIG. 2A. The stack height SH is influenced by the apex angle α, which characterizes the angle of the slope region of the second pole 38 near the yoke tip portion 46 measured relative to a horizontal reference such as the intermediate layer 32. Increasing the stack height SH makes it difficult to control the track width within narrow set tolerances, decreasing the production yield. Consequently, increasing the apex angle α has the effect of increasing the stack height SH to the detriment of write performance. 
A further problem associated with the apex angle α relates to the magnetic properties of the second pole 38. Increasing the apex angle α increases the topography over which the second pole 38 must be formed near the yoke tip portion. The second pole 38 is typically formed by sputtering or plating, techniques well suited for producing flat layers, but not as well suited for forming complex surfaces. Consequently, a further problem associated with the apex angle α is lower production yields resulting from the difficulties encountered in producing uniformity in the second pole 38, especially in the slope region. Still another problem associated with apex angle α relates to the magnetic properties of the second pole 38 in the slope region, which will be described with reference to FIGS. 3A–3C.
The trend towards higher density recording in the disk drive industry has forced a number of materials changes in the components of the drives, which has, in turn, created additional problems. In particular, in order to achieve higher data densities on the surface of the magnetic disk 16, the traditional magnetic media have not been found to be sufficient. To obtain smaller bits it has been necessary to develop recording media with higher magnetic coercivities. To write to a magnetic medium with a higher magnetic coercivity requires that the write element 28 produce a stronger fringing flux field. To produce a stronger fringing flux field further requires the use of magnetic materials capable of carrying larger magnetic fluxes. In other words, for high density recording applications, new materials for components of the yoke 41 need to have high magnetic saturation (Bs) values.
Permalloy, a nickel alloy containing 20% by weight of iron, is the material most frequently used to form magnetic components of prior art recording devices. However, Permalloy has an unacceptably low Bs for use in high density recording. Consequently, designers of magnetic recording devices have turned to high Bs materials such as nickel alloys containing between 35% and 55% by weight of iron. Replacing Permalloy with higher Bs materials would be a simple matter except for the issue of magnetostriction. 
When a material with a non-zero magnetostriction is subjected to a stress, a magnetic field is produced in response. Similarly, when such a material is placed in a magnetic field, a stress in the material develops. Permalloy has been an advantageous material in magnetic recording devices because it has a magnetostriction value of nearly zero. The higher Bs materials, on the other hand, exhibit much higher magnetostriction values. These higher magnetostriction values create additional problems for high density recording applications.
FIGS. 3A–3C illustrate how the apex angle α coupled with high Bs materials is problematic for high density recording. FIG. 3A shows a plan view of the second pole 38 showing a typical arrangement of magnetic domains 51 as they appear on the top surface of the second pole 38 when fabricated from high Bs materials. Arrows within the magnetic domains 51 indicate the orientations of the domains' magnetizations. Through much of the body of the second pole 38 the magnetic fields of the domains 51 are favorably oriented perpendicular to the long axis of the second pole 38. However, in the second pole tip region 45 the magnetization of domains 51 are aligned parallel to the long axis of the second pole 38. In the intervening slope region, the magnetic domains are disordered.
FIG. 3B shows a cross-sectional view along the line 3B—3B of FIG. 3A. Similarly, FIG. 3C is an ABS view along the line 3C—3C of FIG. 3B. In FIG. 3C the orientations of the magnetization within the magnetic domains are represented by dots and circled dots. Dots and circled dots show, respectfully, orientations into and out from the plane of the drawing. From FIGS. 3A–3C it can be seen that within the second pole tip region 45 the magnetic domains form a layered structure with magnetization orientations perpendicular to the ABS. This layered structure is sometimes referred to as a striped domain pattern.
It has been found that with increasing apex angle α the stresses in the magnetic film in the slope region of the second pole 38 also increase. Some of the stress in the magnetic film  is inherent from the manufacturing process. Additional stresses may increase during the operation of the read/write head 24 as heat is generated within the device and differences in coefficients of thermal expansion between different materials create minor dimensional changes. The retention of photoresist as an insulator in some prior art devices is especially troublesome in this regard, as photoresist has a relatively large coefficient of thermal expansion. Consequently, photoresist retained beneath the second pole 38 has the effect, when the device is in use, of creating especially large stresses in the slope region of the second pole 38. Therefore, since the effect of magnetostriction is to counteract a stress with a magnetic field, undesirable magnetic fields in the slope region of the second pole 38 tend to increase both as the apex angle α increases and when photoresist is retained beneath the second pole 38. These undesirable magnetic fields give rise to the striped domain pattern and disordered domains.
The striped domain pattern in the second pole tip region 45 and the disordered domains in the slope region are detrimental to the performance of the write element 28. In particular, these misoriented domains resist changes in the magnetization of the yoke 41. Consequently, when a write current is introduced into the coil layer 48 and a magnetic field is induced in the yoke 41, the flux rise time is lengthened by the resistance to change of the misoriented domains. Longer flux rise times and poorer performance are, therefore, associated with an increasing apex angle α and with the use of retained photoresist beneath the second pole 38.
FIG. 4 shows a more desirable arrangement of magnetic domains 51 for the second pole 38. Arrows within the magnetic domains 51 indicate magnetic orientation. With such an idealized arrangement, the magnetization of the yoke 41 should respond more quickly to changes in the write current in coil layer 48, thus improving the write performance of the write element 28 by reducing the flux rise time. 
Thus, what is desired is a write element with a substantially flat second pole and a shorter yoke length YL. Such a write element would eliminate the apex angle α, have a smaller stack height SH, and would not have the misoriented magnetic domain problems associated with the slope region. Further, it is desired to be able to fabricate a write element without retaining any photoresist as an insulator. It is additionally desired that fabrication of such a write element should be inexpensive, quick, and simple. 